Speaker
Description
Real photon-scattering experiments are a well-established technique to investigate dipole-excitation modes due to the low angular-momentum transfer of photons [1-3]. On the one hand, the usage of an energetically-continuous $\gamma$-ray beam enables the determination of absolute transition strengths in a broad energy range. On the other hand, $\left(\gamma,\gamma'\right)$ experiments utilizing a quasimonoenergetic and linearly-polarized photon beam allow for the assignment of the radiation’s character to the observed transitions and the investigation of total photoabsorption cross sections. Therefore, the combination of these complementary measurements exhibit the complete study of the dipole response below the particle-separation threshold.
For gaining a better understanding of the different dipole-excitation modes of atomic nuclei, systematic studies using different probes on the same nuclide (multimessenger approach [4]) or using the same probe along, e.g., isotopic and isotonic chains are crucial. For the latter one, the proton-magic nickel isotopic chain (Z = 28), which consists of four even-even, stable isotopes with N/Z ratios between 1.07 and 1.29, is well suited. The dipole response of $^{58,60}Ni$ has already been investigated by analyzing real photon-scattering data [5-7]. In addition, the unstable isotopes $^{68,70}Ni$ were measured in Coulomb-excitation experiments in inverse kinematics for studying the low-lying dipole response [8-10].
One missing link for completing the systematics is the investigation of the most neutron-rich, stable Ni isotope $^{64}Ni$. Hence, both aforementioned types of complementary $\left(\gamma,\gamma'\right)$ experiments were performed on this isotope.
In this contribution, the experiments and first results will be presented.
This research is supported by the BMBF [05P21PKEN9].
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[7] M. Scheck et al., Phys. Rev. C 88, 044304 (2013).
[8] O. Wieland et al., Phys. Rev. Lett. 102, 092502 (2009).
[9] D.M. Rossi et al., Phys. Rev. Lett. 111, 242503 (2013).
[10] O. Wieland et al., Phys. Rev. C 98, 064313 (2018).
